Toothed belts used for driving a camshaft of an internal-combustion engine of an automobile are required to have high dimensional stability to keep suitable timing. Furthermore, rubber belts used for, for example, driving an injection pump, etc. and transmitting power in industrial machines are required to have strength and elasticity that allow the rubber belts to withstand a heavy load and severe bending. In order to fulfill these requirements, a rubber-reinforcing cord including a reinforcing fiber is embedded in the matrix rubbers for these rubber products in some cases. Also, as a means for reinforcing the toothed belt, a rubber-reinforcing sheet including a reinforcing fiber sheet is used in addition to the rubber-reinforcing cord in some cases.
On the other hand, belts made of chloroprene rubber conventionally have been used for industrial applications, such as office automation apparatuses. With the dioxin issue having been discussed in recent years, use of the chloroprene rubber has been shifted positively to use of ethylene-α-olefin rubber, such as ethylene-propylene rubber (EPR) and ethylene-propylene-diene monomer copolymer rubber (EPDM), that is free from halogen. However, the ethylene-α-olefin rubber has low adhesion particularly to fibers used as a reinforcing material for rubbers. This tends to cause a problem such that the fiber is separated easily from the rubber while being used.
In order to enhance the adhesion between the matrix rubber and the reinforcing fiber, and furthermore, in order to prevent deterioration of the quality of the reinforcing fiber, a coating film to be provided on a surface of the reinforcing fiber has been studied.
For example, JP 8 (1996)-113657 A discloses a rubber-reinforcing cord on which a coating film is formed by applying a treatment agent obtained by mixing a resorcin-formaldehyde condensate and a styrene-butadiene-vinylpyridine latex to a reinforcing fiber.
On the other hand, from the viewpoint that use of a large amount of resorcin-formaldehyde condensate and ammonia increases an environmental burden and necessitates environmental measures to be taken particularly for workers, JP 1(1989)-272876 A discloses a rubber-reinforcing cord on which a rubber layer free from a thermosetting resin component, such as a resorcin-formaldehyde condensate, is formed as a coating film by treating a reinforcing fiber only with a rubber latex.
JP 2004-183121 A proposes a rubber-reinforcing cord on which a coating film is formed using an aqueous adhesive containing a hydrogenated nitrile rubber latex and a maleimide crosslinking agent, as a rubber-reinforcing cord having satisfactory adhesion to a predetermined rubber, a high heat resistance, and a high bending fatigue resistance.
JP 7 (1995)-217705 A discloses, as a tooth cloth constituting a toothed belt, a tooth cloth (a rubber-reinforcing sheet) that is treated with a solution obtained by mixing a resorcin-formaldehyde condensate and a latex and then is impregnated with a rubber cement containing a filler such as carbon. In addition, JP 7 (1995)-259928 A discloses a tooth cloth treated with a rubber composition obtained by mixing a hydrogenated nitrile rubber and N,N′-m-phenylenedimaleimide.
However, it is difficult even for the rubber-reinforcing cord described in JP 8 (1996)-113657 A to obtain an adhesive strength sufficient to meet the current demands. Also, the rubber-reinforcing cord described in JP 8 (1996)-113657 A causes a heavy environmental burden due to a large amount of resorcin-formaldehyde condensate with which the reinforcing fiber is treated.
The rubber-reinforcing cords disclosed in JP 1(1989)-272876 A and JP 2004-183121 A use neither a resorcin-formaldehyde condensate nor ammonia. In some cases, however, they cannot have satisfactory adhesion to rubber depending on the type of the rubber used, for example, ethylene-α-olefin rubber with a light environmental burden.
The rubber-reinforcing sheets described in JP 7 (1995)-217705 A and JP 7 (1995)-259928 A cannot have satisfactory adhesion to rubber in some cases depending on the type of the rubber used, for example, ethylene-α-olefin rubber with a light environmental burden.
Treatment agents for glass fibers also have been proposed. For example, JP 2007-70169 A discloses a glass fiber binder containing a polymer obtained by graft polymerization of vinyl pyrrolidone onto polyvinyl alcohol, as a binder for enhancing the binding of the glass fibers. JP 2004-203730 A discloses a glass fiber coating solution containing an acrylic acid ester resin, a styrene-butadiene-vinylpyridine copolymer, and a resorcin-formaldehyde condensate resin, as a glass fiber coating solution used for forming a coating layer for a rubber-reinforcing glass fiber. The acrylic acid ester resin contained in this coating solution is an acrylic acid ester emulsion obtained by adding polyvinyl alcohol or modified polyvinyl alcohol to an acrylic monomer as a water-soluble colloid, and then emulsion-polymerizing it. However, even when a reinforcing cord is formed using a glass fiber that has been treated with any of these treatment agents, satisfactory adhesion to rubber cannot be obtained in some cases depending on the type of the rubber used.